Hydroxamate siderophores of root nodule bacteria

Sixty strains of root nodule bacteria were screened for siderophore product ion in low-iron broth, among them 40 strains from the Australian Inoculants Research and Control Service (AIRCS) which are the current commercial inoc ulants used in the pulse and legume pasture industries in Australia. Eleven new siderophore-producing strains were recognised including Sinorhizobium meliloti (WSM826. WSM352, SU47), Rhizobium leguminosarum boivar viviae (WU1 63, MNF3841, SU391), Rhizobium leguminosarum boivar trifoli (CB782, CC2483g , CC383b) and Rhizobium tropici (WSM1385, CB3060). Siderophores were identi fied by chemical characterisation for catecholate or hydroxamate, spectral studies, isoelectrofocusing and siderophore-mediated iron-uptake studies. T he S. meliloti strains all produced dihydroxyamate siderophores. Other side rophore-producing rhizobia, with the exception of R. tropici CB306c, excret ed trihydroxamate-type siderophores. No bradyrhizobia were Chromazurol S-po sitive. Fe-59 uptake studies revealed that all strains transported iron com plexed to citrate. The sinorhizobia tool; up 5-10-fold more iron from dihyd roxamate than trihydroxamate siderophores. Conversely, other rhizobia and t he slow-growing bradyrhizobia transported iron complexed to trihydroxamates at rates 2-5 fold those of dihydroxamate siderophores. Rhizobactin 1021 wa s excreted by S. meliloti strains 1021, Rm2011 and SU47 and vicibactin by s even strains of R. leguminosarum (bv. viciae and bv. trifolii). (C) 2000 El sevier Science Ltd. All rights reserved.